A "caring, unassuming and conscientious" hospital nurse took out his frustrations by poisoning and murdering patients, a court has heard.

Victorino Chua had a "malign intention to cause havoc" acting in a way that was "impossible to fathom", the jury at Manchester Crown Court heard.

The 49-year-old is accused of murdering three patients and harming 18 others by poisoning them with ampoules and saline drips contaminated with insulin while working on two wards at Stepping Hill Hospital in Stockport in June and July 2011.

After police were called in he allegedly "changed tack" by sabotaging prescription charts, doubling and trebling dosages, leading to his arrest in January 2012.

Filipino Chua, a father-of-two, denies all the offences but after three months of evidence prosecutor Peter Wright QC, in his closing speech to the jury said the poisonings were not "naturally occurring phenomena" but the work of the defendant.

He said: "What may lead an otherwise caring, unassuming and conscientious nurse to act as we say he did is impossible to fathom.

"Why anyone should behave in that way is beyond comprehension.

"What makes someone contaminate products detrimental to the health and survival of others is impossible to rationalise."

Mr Wright told the jury they may find an "insight into his deeply complex thought processes that might be at work" in the self-penned letter found at his home after his arrest.

In the letter, described as "the bitter nurse confession" by Chua, the nurse said he was "an angel turned into an evil person" and "there's a devil in me", who had things he would "take to the grave."

Mr Wright told the jury: "We say this letter in the form of auto-biography, was a living and unfinished document.

"There was unfinished business. It is a narrative of his life, of his feelings, of his pent up frustrations. It was a portent of things to come and of what he had done.

"It is an insight into his thought process during a period of considerable anger and disharmony both at home and at work which co-incided with these events.

"The evidence points sadly to a man who, for reasons truly known only to himself, decided to take out his frustrations on his and other's patients.

"To play with their health and ultimately existence, and future well being, knowing what he was doing, knowing how lethal the administration of insulin was to the health and well being of a patient, choosing nevertheless to act as he did."

The jury then heard from Peter Griffiths QC, defending Chua.

He began: "It is our submission, I say this perfectly quietly and straightforwardly, that Victorino Chua is kind, considerate and conscientious.

"We say he is a man who has been wrongly singled out, I'm going to use an expression you will recognise, he's been singled out to carry the can.

"Back in January, three months ago, I used the term scapegoat. I unhesitatingly repeat it. That's our position."

Mr Griffiths said the effort the police had put into the investigation resulted in "huge pressure" to bring someone to account, given the initial arrest, charging then releasing of another nurse and colleague of the defendant's.

He continued: "Of course they arrested Rebecca Leighton earlier on.

"She was kept in prison for a month or so. But they have latched on to a man and really tried to look at every conceivable thing adverse to him they can throw at him, stir it up and say, 'He's the guy.'"

The jury were reminded none of Chua's fingerprints were found on any of the contaminated ampoules or saline bags - and no one has seen him allegedly sabotaging any products while working at the hospital.

Mr Griffiths reminded the jury of the "history" of the case.

Contaminated ampoules were first discovered in July 2011 and Ms Leighton arrested and charged later that month.

She was then released and the case against her dropped in September 2011.

Chua was then interviewed six times by police - and was "fully co-operative" throughout, until altered prescription charts were discovered in January 2012 when he, along with others, had been on duty.

Mr Griffiths said: "He had the misfortune to be in the wrong place at the wrong time."

After his arrest Chua did not go "no comment" in interview with detectives, but was questioned for more than 15 hours by police - answering all their questions, the jury were told.

Mr Griffiths said if the prosecution had an "overwhelming" case of guilt - why was Chua then released on bail for two years before he was charged with the offences.

"Does that history fill you with any confidence that the prosecution has got the right guy?" he asked the jury.

Chua has pleaded not guilty to 36 charges in all, including the murders of Tracey Arden, 44, Derek Weaver, 83, and Arnold Lancaster, 71, one count of grievous bodily harm with intent, 23 counts of attempted grievous bodily harm, eight counts of attempting to cause a poison to be administered and one count of administering a poison.